staging: greybus: loopback: Fix iteration count on async path

Commit 12927835 ("greybus: loopback: Add asynchronous bi-directional
support") does what it says on the tin - namely, adds support for
asynchronous bi-directional loopback operations.

What it neglects to do though is increment the per-connection
gb->iteration_count on an asynchronous operation error. This patch fixes
that omission.

Fixes: 12927835 ("greybus: loopback: Add asynchronous bi-directional support")

Signed-off-by: Bryan O'Donoghue <pure.logic@nexus-software.ie>
Reported-by: Mitch Tasman <tasman@leaflabs.com>
Reviewed-by: Johan Hovold <johan@kernel.org>
Cc: Alex Elder <elder@kernel.org>
Cc: Mitch Tasman <tasman@leaflabs.com>
Cc: greybus-dev@lists.linaro.org
Cc: devel@driverdev.osuosl.org
Cc: linux-kernel@vger.kernel.org
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>